The invention concerns a method of producing marking on a surface by means of laser radiation.
In this specification the term marking means any suitable kind of marking such as decoration, labelling, addressing, captioning, inscription and the like.
One form of method of producing marking or the like on a surface by means of laser radiation comprises successively applying to the surface at least two differently colored layers of colored lacquer. The first or outer layer lacquer, which is thus remote from the surface and which faces towards a person viewing the article providing that surface, is removed by means of the laser radiation in a region-wise manner to produce the appropriate marking on the surface, by virtue of the differently colored second layer lacquer therebeneath being exposed.
A method of that nature may be used more especially for example when the situation involves providing precise and accurate markings such as decoration or labelling on articles which are individual parts or which are produced only in small numbers. The laser beam which is used to burn away the first or outer layer of colored lacquer can be easily controlled with a very high degree of accuracy, in respect of its path of movement, for example by means of an electronic computer. In that operation it is also possible to vary the thickness of the line which is produced by the laser beam burning away the material of the outer layer of colored lacquer. Suitable equipment for carrying out that method is available and is offered for example by Baasel Lasertech.
A method of producing safety markings on a surface can also be found in EP 0 383 956 Al, in which a colored layer which is covered by an upper laser radiation-absorbent layer is suitably exposed by removal of the upper layer in a region-wise manner, using a laser beam, but there is no information about the mode of applying the layers to the surface in question.
Hitherto, the operating procedure adopted has been such that the surface on which a marking is to be produced, for example the front plate of a piece of equipment, has been provided with two differently colored layers of lacquer, using conventional application procedures. The upper or outer layer of lacquer is then removed and the underneath layer of lacquer which contrasts in color with the outer layer of lacquer is exposed in a configuration corresponding to the desired marking such as a desired decorative or patterning effect, labelling, caption or the like. In that situation however the problem which arises is that the conventionally applied layers of lacquer suffer from variations in thickness, with the result that, when the outer layer of lacquer is burnt away by means of the laser beam, under some circumstances the outer layer may not be completely removed in the regions in which it is relatively thick. If a higher level of laser power is used, it is then admittedly possible to ensure that the outer layer of lacquer is reliably removed, even where it is of relatively greater thickness. In that case however there is then the risk that the underneath layer of lacquer may also be affected to a considerable degree by the laser beam, in regions in which the outer layer of lacquer is relatively thinner, and the effect on the underneath layer of lacquer may be to such a degree that the underneath layer of lacquer is at least seriously damaged or even completely removed. A further danger which arises is that, if the layers of lacquer are of different thicknesses, the line produced by means of the laser beam, in spite of the level of laser power remaining at least substantially constant, may be of different widths or strengths, so that, as will be readily appreciated, the appearance of the correspondingly marked surface is also adversely affected in that way. In order to produce acceptable and useful laser marking or decoration or the like, it was therefore necessary hitherto to apply the outer layer of lacquer, namely that which is to be subsequently removed in a region-wise manner by the laser beam, with a thickness which is as uniform as possible. It will be appreciated however that that resulted in a quite inconsiderable increase in the cost of manufacture of articles requiring a marked surface of that kind so that hitherto laser marking was only used for a few areas, more particularly for example in relation to very expensive or high-quality equipment.